1. Field of the Invention
The present invention is related to computer systems in which power is supplied to multiple devices from one or more common power supplies, and more specifically to energy management techniques that permit reduction of overhead in the power supply by locally limiting power supply current provided to the devices using soft switches.
2. Description of Related Art
In computer peripheral subsystems, and in other subsystems such as storage subsystems, in which devices may be added or removed to I/O connections, power is also distributed using the I/O connectors or using additional power bus connectors. Examples of such connections are as card rack connectors, e.g. peripheral component interconnect (PCI) or PCI extended (PCI-X) bus connectors or PCI-Express (PCI-e) connectors. Power is also distributed in systems using external cabled connectors such as IEEE-1994 interfaces or universal serial bus (USB) interfaces.
In subsystems in which an unknown or potentially variable group of devices may be attached to such power connections, the potential current that is maintained in availability to the power distribution system is necessarily higher than that actually used by the totality of the devices. In general, there is a significant amount of overhead, because either the maximum current that may be required by a group of devices is set at a multiple of the per-device maximum power specification for the particular I/O interface or associated power connection by the number of connections available, or by the number of devices actually present. In many such systems, multiple power supplies are used to provide current to the power distribution system and if only a relative few devices are installed, or the installed devices are mostly low-power devices, a power supply may be needlessly operating, reducing system efficiency and potentially lowering reliability. Finally, in installations such as server and storage racks, multiple air moving devices (AMDs) may be operated to handle the maximum possible generated heat, and in the above low power usage examples, operation of all of the AMDs may be unneeded, with the resultant cooling overhead also reducing system energy efficiency and additionally raising ambient noise levels.
Therefore, it would be desirable to provide a energy management method and energy management system that reduces the current and or cooling overhead in a power distribution system.